Does morning sickness mean a girl?

Partly true, but only for severe sickness, and only by a little. In large studies, women hospitalised for severe vomiting had slightly more girls: about 54% girls instead of the usual 49%. For ordinary nausea the link is weak or absent, so it can't tell you about your own baby.

This is one of the few old wives' tales with real data behind it. But the effect is small. Even in the strongest case it moves the odds from a coin flip to a slightly weighted coin.

The verdict

The old wives say

👶 GIRL

severe morning sickness → slightly more likely a girl

At best ~54% girl — barely more than a coin flip

Want a real read? BabyPeek checks your ultrasound with 5 methods.

See it in the app

What the studies found

  • Sweden, 1999 (The Lancet). Among mothers treated for hyperemesis gravidarum (HG), the severe form of pregnancy sickness, there were more girls than expected.
  • Denmark, 2001. A national registry covered 6,227 births after a hospital diagnosis of HG, 1980–1996. There were 0.87 boys for every girl, against 1.04 in the general population.
  • Meta-analysis, 2011. Pooling the published studies, women with HG were more likely to have a girl, with an odds ratio of 1.27.
  • Japan, 2019. The Japan Environment and Children's Study asked 91,666 women about nausea before 12 weeks. 82.7% had at least some symptoms and 11.1% had severe symptoms. Women carrying girls had higher odds of both.
  • USA, 1999. A small study of 104 women found morning sickness was not systematically related to the baby's sex.

What "more girls" means in real numbers

"Associated with girls" sounds bigger than it is, so here is the Danish figure as a percentage.

  • In the general population there were 1.04 boys per girl. That is about 51% boys and 49% girls.
  • After severe, hospital-treated sickness there were 0.87 boys per girl. That is about 46.5% boys and 53.5% girls.

So among women sick enough to be admitted to hospital, the chance of a girl rose by roughly five percentage points. Most women with morning sickness are never admitted, and for them the shift, if any, is smaller still.

Why there might be a link

The most discussed explanation is hCG, the pregnancy hormone that pregnancy tests detect. It is thought to be one of the contributors to nausea. A 2025 study of 1,052 pregnancies found higher first-trimester free β-hCG in pregnancies with a girl. If girls tend to come with slightly more hCG, a slight lean toward more nausea would fit.

But hCG levels vary widely between women, and many other things affect nausea. The difference between boy and girl pregnancies is small next to that variation.

Why it can't tell you about your baby

More than four in five pregnant women in the Japanese study had some nausea, whatever the baby's sex. Mild or moderate sickness is common with boys and girls alike, and many women carrying girls feel fine. A link that shows up across tens of thousands of births barely moves the odds for any one pregnancy.

If you enjoy the tale, enjoy it, and keep the nursery paint neutral. For more folklore put to the test, see old wives' tales for baby gender.

When sickness needs a doctor, not a prediction

If you can't keep food or fluids down, are losing weight, feel dizzy or are passing very little urine, contact your doctor or midwife. Severe pregnancy sickness is a medical condition that can be treated. Its link to the baby's sex is the least important thing about it.

Methods that look at the baby

If you want more than folklore, these use your actual scan: nub theory at 11–13 weeks and ultrasound signs. The Chinese calendar is another bit of fun, though it has been tested and does no better than chance.

How BabyPeek does it

In BabyPeek you measure the nub and mark the placenta side on your own scan, answer the skull-theory questions, and the app adds the Chinese calendar and a playful Photo Pick. It labels how much evidence each method has, shows one majority verdict and turns it into a shareable reveal.

Download on theApp Store

FAQ

Only slightly, and mainly for severe, hospital-treated sickness. In Danish data about 53.5% of those babies were girls, against about 49% in general. That is not enough to predict one pregnancy.
It is linked to girls in several large studies, with an odds ratio of about 1.27 in a 2011 meta-analysis. Plenty of women with hyperemesis still have boys.
Yes. Many women carrying girls have little or no sickness, and many carrying boys are very sick. The overlap is large.
One idea is hCG. A 2025 study found slightly higher first-trimester hCG in pregnancies with girls, and hCG is thought to contribute to nausea. The difference is small compared with how much hCG varies between women.
If you can't keep food or fluids down, are losing weight, or feel faint or dehydrated. Severe pregnancy sickness is treatable.

Sources

  1. Askling J, Erlandsson G, Kaijser M, Akre O, Ekbom A. Sickness in pregnancy and sex of child. Lancet. 1999;354(9195):2053. PubMed
  2. Basso O, Olsen J. Sex ratio and twinning in women with hyperemesis or pre-eclampsia. Epidemiology. 2001;12(6):747–9. PubMed
  3. Veenendaal MV et al. Consequences of hyperemesis gravidarum for offspring: a systematic review and meta-analysis. BJOG. 2011;118(11):1302–13. PubMed
  4. Mitsuda N, Eitoku M, Maeda N, Fujieda M, Suganuma N. Severity of nausea and vomiting in singleton and twin pregnancies in relation to fetal sex: the Japan Environment and Children's Study. J Epidemiol. 2019;29(9):340–6. PubMed
  5. Perry DF, DiPietro J, Costigan K. Are women carrying "basketballs" really having boys? Testing pregnancy folklore. Birth. 1999;26(3):172–7. PubMed
  6. Parisi F et al. Impact of fetal sex on first trimester markers of placental development and pregnancy outcome: a prospective cohort study. Eur J Obstet Gynecol Reprod Biol. 2025;315:114735. PubMed

Written by the BabyPeek editorial team from the studies above. How we research and write. For entertainment, not medical advice.